Effect of some enzyme inhibitors on ATP level and hypersensitive reactivity of potato tuber disks to incompatible race of Phytophthora infestans.

Abstract

Sodium azide (NaN3), 2, 4-dinitrophenol (2, 4-DNP), blasticidin S (BcS), p-chloromercuribenzoic acid (PCMB) and dextran (MW. 7×104)-bound p-chloromercuribenzoic acid (PM DT) are known to inhibit the rapid occurrence of hypersensitive death of cells infected by an incompatible race of Phytophthora infestans. Among these enzyme inhibitors, NaN3 and 2, 4-DNP have been supposed to inhibit the hypersensitive cell deaht by reducing ATP levels. In the present experiments, ATP contents in the potato tuber disks treated with these inhibitors were determined by using the luciferin-luciferase methods. Thin disks 0.5 mm thick, which consist of 2.3 cell layers in average, were used, so that almost all of the total cells were exposed to the inhibitors. Therefore, the analytical results were thought to indicate ATP levels in the cells exposed directly to the inhibitors. Experiments showed that 2, 4-DNP and NaN3 reduced ATP level and also inhibited hypersensitive cell death upon infection when aged disks were treated. When the fresh disks were treated with 2, 4-DNP or NaN3 and then ATP contents were determined 20 hr after the treatment, ATP levels remained low only in the former case, while in the latter almost the same level as the water-treated disks was regained. At one day after treatment of the fresh disks with 2, 4-DNP or NaN3, the potential of hypersensitive reactivity (hypersensitive cell death) was low in the former and high in the lattter. PCMB and PMDT did not reduce the ATP level but inhibited the hypersensitive cell death. BcS also failed to reduce the ATP level. These results were consistent with the presumption that BcS inhibits the development of the potential to react hypersensitively to the incompatible race, that PCMB and PMDT inhibit the hypersensitive cell death through a mechanism other than the inhibition of ATP generation, possibly by affecting the cell membrane, and that NaN3 and 2, 4-DNP may inhibit the hypersensitive cell death by inhibiting ATP generation.